Photographic silver halide diffusion transfer process



2,987,396 PHOTOGRAPHIC SILVER HALIDE DIFFUSION TRANSFER PROCESS Leslie A. Williams and John D. Knowles, Harrow, England, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Dec. 29, 1958, Ser. No. 783,129 7 Claims. (Cl. 96-29) This invention relates to photographic process for producing direct positive images and to materials for use therein.

In photography, most of the layers in which photographic images are found are themselves originally lightsensitive. However, not all photographic layers used for forming images are light-sensitive and the present invention concerns a class of non-light-sensitive layers, namely, those containing development nuclei for silver salts, or substances forming development nuclei at a suitable stage in the photographic process or precipitants for silver salts by double decomposition. Such non-light-sensitive layers are used to form positive silver or silver salt images therein by reaction between the substances in the layers and dissolvedsilver salts dill-using thereinto from a contiguous silver halide emulsion layer which has been ex- United States Patent posed image-wise and which has been or is being developed to a negative image.

One drawback sometimes encountered in processes of this type is that the positive image produced is of a brownish or other non-acceptable colour.

The present invention provides a sheet material comprising a non-light-sensitive photographic layer containing a silver precipitating agent such as development nuclei, or a substance capable of forming development nuclei with dissolved silver salts, and also containing an oxazoline-Z-thiol of the following general formula:

wherein R and R each represents hydrogen or a lower alkyl group such as methyl, ethyl, propyl or butyl.

The invention includes the process of preparing a direct positive image which comprises exposing a photographic silver halide emulsion layer to an object or image, developing a negative image in the exposed layer, and, during or after development, transferring silver halide from the undeveloped or unexposed areas of the emulsion layer to a non-light-sensitive image-receiving layer containing a silver precipitating agent such as development nuclei or a substance capable of forming de velopment nuclei with dissolved silver halide and in effective contact with the emulsion layer, the transfer being effected in the presence of a silver halide solvent and an oxazoline-Z-thiol of formula above.

By in efiective contact, we mean that dissolved silver salts can diffuse from the emulsion layer to the non-lightsensitive layer. There may be an intermediate layer present between the two aforesaid layers which does not hinder the silver salt diffusion, and the two layers may or may not be coated on the same support. Thus, the oxazoline-Z-thiol may be present in the reception layer of a sensitive element such as described in the Yackel et al. US. patent application Serial No. 586,705, filed May 23, 1956, wherein a support is provided with a reception layer containing a silver precipitating agent such as colloidal silver or silver sulfide, and thereover a silver halide emulsion the colloid vehicle of which is an alkalisoluble cellulose ether phthalate facilitating the removal of the emulsion following formation of the positive image in the reception layer.

We have found that the presence of oxazoline-Z-thiol has the effect of producing a blacker positive image than would otherwise be produced.

In the process of the invention the oxazoline may be present in the receiving layer or in the solution employed for elfecting development in the emulsion layer, or it may have been incorporated in the emulsion layer before exposure.

An alkaline solution is used to etfect development of the exposed layer and the developing agent may be present in either the emulsion layer or in the alkaline solution or both. A mixture of developing agents may be used, if desired.

The silver halide solvent may be present in the developing solution or the receiving layer and is preferably sodium thiosulphate.

It is preferable to employ an antifoggant to prevent the formation of fog in the exposed emulsion layer and this may be present in either the emulsion layer or in the alkaline solution used to effect development. Any of the well-known nitrogen-containing organic antifoggants may be used and it has been found that the benzotriazoles are very suitable.

The oxazoline-Z-thiols employed in the present invention may be prepared by the method described in J.A.C.S., 1952, 74, 2994, and J.A.C.S., 1937, 59, 2013. Examples of those compounds are oxazoline-Z-thiol, 4- ethyloxazoline-Z-thiol, S-methyloxazoline-Z-thiol. When employed in the receiving layer, they are preferably incorporated in an amount of between 2 and 20 gms./sq. m. such as about 5 gms./sq. in. When employed in the developing solution, they are preferably incorporated in a concentration between 7.5 and mgs./litre.

A suitable non-light-sensitive layer for use in the present invention comprises a gelatin layer containing a substance constituting development nuclei (such as colloidal silver or silver sulphide) or a substance forming development nuclei with dissolved silver salts (such as zinc sulphide), and also containing one of the oxazoline-Z- thiols of the invention.

Such a layer may be coated on a paper support and contacted with an exposed and developing emulsion layer coated on a separate support in the presence of a silver halide solvent, or may be coated on the same support as the emulsion layer. In the latter case, it is preferable to coat the non-light-sensitive layer on a paper support, then to overcoat this layer with a comparatively unhardened emulsion layer. After exposure, development and formation of the direct positive image in the non-lightsensitive layer, the exposed and developed unhardened emulsion layer is removed, for example by washing in warm water.

The following examples illustrate the present invention.

Example 1 A high contrast silver chloride emulsion containing the following constituents is coated on a paper support at the mentioned coating rate.

Grams/sq. rn.

Silver chloride 1.4 Diphenyl iodonium-S-methyl benzotriazolid 0.063 Hydroquinone 0.28 Gelatin 5.6

The resulting emulsion layer is exposed to a subject Water to 1 litre.

' 11g"-ofaftetfievItipment, theei emulsion layer "containing developing 'ag'e'nt' is Squeegees for about 20 seconds into contact with an image-receiving sheet comprising a paper support bearing a nucleated layer as follows:

oramslsqj 'm. Gelatin v 6.2 Sodium thiosulphate (anh.) 1.4 Titanium dioxide 0.63 Colloidal silver sulphide 0.004 Oxazoline 2 thiol (1075 After separating the layer and the-sheet, a positive image of a-good black colour was obtained on the receiving sheet.

Example 2 The procedure of Example 1 was'repeate'd' with the single exception' that the oxaz'oline-2 thiolemployed in =1-phenyl-3-pyrazolidone 0.5.

Potassium bromide 0.5 -methyloxazoline-2-thiol'4"; 0.02

Water to 1 litre.

While development was still proceeding the layer was 'squeegeed into contact with an image-receiving sheet comprising. a paper support bearing anucleated layer as follows:

. Grams/sqnm. Gelatin r e Y t 6.2 Sodium thiosulphate (anh.) 1.4 Titanium dioxide w 0.63

v Colloidal silver sulphide 0.004

After leaving the emulsion layer and nucleatedlaye r in contact for about 20 seconds, they were separated, and a positive image of the original of a good black colour was obtained on the receiving sheet.

What we claim is:

1. A process'for preparing 'a photographic silver image of improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferring the silver halide from the undeveloped areas of theem'ulsion layer tovan imagereceiving layer containing a silver precipitating agent, the transfer being efiected in contiguity with a silver halide solvent and an oxazoline-Z-thiol.

2. A process for preparing a photogra'phic silver image of improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferringthe silverhalide from the undeveloped areas of the emulsion layer to an image-receiving layer containing a silver precipitating agent the transfer being efiected in contiguity with a silver halide solvent and 'a compound of the class consisting of oxaz'oline-2 thiol, 4'-et1iy16xazo1ine'-2-thio1, and 5- methyloXazoline-2-thiol. I .7 V

3. A process 'for'preparin'g'a photographicsilver image of improved tone which comprises" exposing a photographic silver halide emulsionl'ayerto asubject, developing' the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an imagereceiving layer'cont'aining a' silver precipitating agent, the transfer being efiected in contiguity with a silver halide solvent and oXazolin'e-2-thiol. l t a 4. A process for preparingaphotegraphie'siwer image .of improved, tone which comprises exposinga photographic silver'halid'e emulsion layer to a'subjec't, developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an imagereceiving layer containinga silver precipitating'ag'ent', the transfer being effected in contiguity'with a silver halide solvent and 4-ethyloxazoline 2-thiol,

5. A process for preparing a photographic silver image of improved tone which comprises exposing a photographic silver halide emulsionlayer to' a subject, developing the emulsionlayer, transferring the silver halide from the undeveloped areas of the'emulsion layer to an imagereceiving layer containing a silver precipitating agent, the transfer being effected in contiguity with a silver halide solvent and 5-methyloxazoline-2-thiol.

6. The process of claim 1 wherein the oxazoline-Z- thiol is present in the developer solution during the transfer step.

7. The process of claim 1 wherein the oxazoline-2-thiol is present in the image-receiving layer during the transfer step.

References Citedin the file ofthis patent UNITED STATES PATENTS 

1. A PROCESS FOR PREPARING A PHOTOGRAPHIC SILVER IMAGE OF IMPROVED TONE WHICH COMPRISES EXPOSING A PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER TO A SUBJET, DEVELOPING THE EMULSION LAYER, TRANSFERRING THE SILVER HALIDE FROM THE UNDEVELOPED AREAS OF THE EMULSION LAYER TO AN IMAGERECEIVING LAYER CONTAINING A SILVER PRECIPITATING AGENT, THE TRANSFER BEING EFFECTED IN CONTIGUITY WITH A SILVER HALIDE SOLVENT AND AN OXAZOLINE-2-THIOL. 